Nephronectin-dependent signaling in kidney development

描述（由申请人提供）：本资助的总体目标是了解一种名为nephronectin的新型细胞外基质蛋白在肾脏发育中的作用。在之前的研究中，我们已经证明，绝大多数缺乏整合素8亚基的小鼠不能发育后肾，其初始表型是输尿管芽向后肾间质生长缺陷，而后肾间质是整合素的表达部位。我们已经确定nephronectin是输尿管芽中表达的一种细胞外基质蛋白，与整合素a8bl相关，并适当分布以激活其配体依赖性信号通路。由于缺乏a8bl的小鼠后肾发育期间的表型与缺乏GDNF-GFRal-c-ret信号通路任何成分的小鼠非常相似，其中配体GDNF在间质中表达，受体亚基GFRal和c-ret在输尿管芽中表达，我们将研究这两种信号通路之间可能的相互作用，并验证缺乏a8bl导致该通路信号传导效率降低的假设。我们将鉴定介导细胞与nephronectin相互作用的受体，并确定发育中的肾脏中哪些细胞类型直接与这种ECM蛋白相互作用。在之前的研究中，通过与细胞骨架的相互作用和胞质信号通路的激活，包括ERK和Jun激酶、PI-3激酶和G蛋白的cd -42/radc-rho家族，整合素的配体参与已被证明可以调节发育的许多方面，包括细胞增殖、迁移、分化和存活。我们将尝试确定哪些途径是由肾连接素参与的a8bl激活的，哪些途径是由于后肾间质中a8bl的缺失而受损的。

DESCRIPTION (provided by applicant): The overall aim of this grant is to understand the role of a novel extracellular matrix protein named nephronectin in kidney development. In previous work, we have shown that the vast majority of mice lacking the integrin a8 subunit fail to develop the metanephric kidney with the initial phenotype of a deficit in ingrowth of the ureteric bud into the metanephric mesenchyrne, the site of expression of this integrin. We have identified nephronectin as an extracellular matrix protein expressed in the ureteric bud that is associated with the integrin a8bl and is distributed appropriately to activate its ligand-dependent signaling pathways. Because the phenotype during metanephric development of mice lacking a8bl is very similar to those of mice lacking any of the constituents of the GDNF-GFRal-c-ret signaling pathway, where the ligand GDNF is expressed in the mesenchyme and the receptor subunits GFRal and c-ret are expressed in the ureteric bud, we will examine possible interactions between these two signaling pathways and test the hypothesis that absence of a8bl results in reduced efficiency of signaling through this pathway. We will identify the receptors that mediate interactions of cells with nephronectin and determine which of the cell-types in the developing kidney interact directly with this ECM protein. In previous work, ligand engagement of integrins by extracellular matrix constituents has been shown to regulate many aspects of development including cellular proliferation, migration, differentiation and survival through interactions with the cytoskeleton and by activation of cytoplasmic signaling pathways including the ERK and Jun kinases, PI-3 kinase, and the cdc-42/radc-rho family of G proteins. We will attempt to determine which of these pathways are activated by nephronectin-engagement of a8bl and which are compromised by the absence of a8bl in the metanephric mesenchyme.